The present invention relates to gamma-radiation detection modules for portal applications and particularly relates to gamma-radiation detection modules for monitoring gamma-radiation emanating from personnel, vehicles, trains, cargo containers and the like.
Existing gamma-radiation detectors used in portal applications are typically either PVT (polyvinyltoluene-based) plastic scintillators or large rectangular NaI(Ti) crystals inside of hermetically sealed housings. In both cases, the detectors utilize photomultiplier tubes to detect photons emitted by the scintillators responsive to impact of gamma-radiation. The PVT-based detectors are used principally because of their relatively low cost. The sodium iodide-based detectors are used primarily for their ability to provide some degree of spectroscopic identification capabilities. Currently, new radiation portals being developed require some degree of spectroscopic identification capability. This means that the use of PVT-based detectors is precluded because the plastic scintillators are unable to provide any energy resolution measurements.
Consequently, sodium iodide-based detectors are preferred since they provide energy resolution measurements. While their costs are higher than PVT-based detectors, the cost of sodium iodide detectors is still lower than many other types of high energy resolution detectors, e.g., high purity germanium, cadmium zinc telluride, high pressure zenon, etc. The drawbacks of sodium iodide-based detectors are that 4-5 detectors must be used to obtain the same detection efficiency as a standard PVT-based portal detector. Additionally, the energy resolution obtainable with these sodium iodide-based detectors is typically 8% at 662 KeV (137-Cs isotope). This means that a tradeoff between energy resolution and cost must be considered when providing a radiation detection portal and the ability to modify or customize detectors for particular portal applications. Accordingly, there has developed a need for a modular, easily manufacturable, high energy resolution gamma detector primarily designed for use in gamma-radiation detection portals.